Flexion contractures or a tendency for muscles, tendons or scar tissue to shorten in skeletal joints are common after trauma and represent a major challenge in the care of such injuries. For example, a contracture of 30.degree.-40.degree. in the elbow can severely reduce upper extremity function.
Contracture and stiffness of the finger joints due to trauma, burns, or arthritis limits the overall function of the hand. Motion of the proximal interphalangeal joint of the finger is especially important, as this joint accounts for more than 50% of the total active motion of the finger.
Current approaches to the treatment of joint trauma have more aggressively sought to prevent contracture and stiffness through movement. Methods of rigid internal fixation with sufficient stability to allow motion within days after injury rather than closed treatment and immobilization in a cast have been developed. In the treatment of dislocations, protected early motion is now begun as soon as the patient is comfortably able to do so.
However, the currently available techniques for the prevention of contracture are not uniformly successful. Early active motion alone can reduce the severity of contracture, but requires the patient's own strength, compliance and constant effort and proper alignment and tracking of the joint cannot be insured. Passive stretching by a therapist can be done on a very limited basis and is applied slowly, but such therapy risks the formation of heterotopic bone and myositis ossifications. Passive stretching is not generally useful at the PIP joint, as it is painful and not uniformly successful. Dynamic splints may be used, but these require pressure on the sometimes sensitive or injured soft tissues, e.g. of the arm and forearm, and may not be possible, i.e. burn injury, or may reduce patient compliance. Examples of such splinting devices include a turnbuckle orthosis or cast, reverse dynamic sling, polycentric cast brace hinges, or a hinged orthoses with rubber band traction.
Continuous passive motion (CPM) devices have been developed which provide early motion gains, but these devices do not normally allow the joint to come to the extremes of motion which are the areas of greatest need. Further, these devices are not designed to insure accurate tracking or stability of the joint, but instead for example, in the elbow device, move the wrist relative to the shoulder or the humerus. These devices also rely on direct pressure on the soft tissues and skin, and thus are subject to the same limitations as the external splints discussed above.
Flexion-extension hinge distractors are hinged external fixators which are designed to hold the joints such as the elbow in distraction while permitting an active range of motion. These include the Volkov elbow hinge-distractor and the Deland and Walker hinge distractor. These devices require the placement of a pin or wire into or in close proximity to the kinematic axis of the elbow, with the pin acting as the mechanical axis of the device. Because these devices are difficult to align over the axis of rotation, pin tracking problems can occur. Furthermore, the mechanical axis cannot be realigned without reinsertion of the pin. In addition, these systems do not permit passive driving of the joint through a range of motion.
An additional problem associated with the flexion-fixation hinge distractors is the placement of pins in close proximity to the joint. Because of the movement of skin over and relative to underlying bone, movement of the skin in this area with normal flexion and extension of the joint in relation to a stationary pin can cause skin irritation and lead to infection. Such placement of the pins may also interfere with the treatment of a fracture by internal fixation.
Contracture and stiffness of the finger joints after trauma is currently prevented by immediate physical therapy of the involved digit. However, it is often difficult to achieve full active motion of the finger because soft tissue swelling and pain prevent the patient from maximal compliance during the critical first weeks of healing. If motion of the injured PIP joint is not initiated and maximized, scar formation around the joint becomes very strong. Later attempts to gain motion at the joint are then prevented by the strength of the scar tissue and the mechanical disadvantage of the passive splint or exercise program. Bony injury or joint instability often precludes actively or passively moving the digit through an effective range of motion, because motion risks redislocation or displacement of the skeletal elements on either side of the joint, or of the joint itself.
Because of limitations with the currently available methods to prevent or treat joint injuries, patients often require surgical soft tissue release to improve the range of motion. Surgical release of contracture must be followed by many months of intensive therapy and splinting to maintain the gains in motion. Such maintenance is not uniformly successful, as the splinting and traditional therapies applied suffer from the same limitations as discussed above. Moreover, oftentimes the cost of surgery and therapy, as well as the costs in time, lost wages and rehabilitation can be significant.